Liquid Culture Systems for in vitro Plant Propagation

Propagation of Prunus and Malus by temporary immersion 249
The water content of temporarily immersed plants decreased at both
immersion times, with the exception of apple at 30 min of immersion. This
trend was also found in most of the plants cultured in stationary liquid
medium (Table 3), in this case, probably because all the plants were
necrotic, except for plum, where the plants appeared hyperhydric. After 60
days, hyperhydricity and necrosis of the explants were never detected in TIS
(Figure 1D), whereas they were present in solid culture. In fact the cherry,
plum and peach controls showed hyperhydricity in 7.5%, 7% and 6% of the
plants respectively, while necrotic apices were present in 11%, 5% and 7%
of plum, peach and apple shoot clusters.
The detrimental effects of stationary liquid culture were also evident in
the content of photosynthetic pigment. On the contrary, TIS stimulated
chlorophyll and carotenoid synthesis at the optimal immersion time, but, in
peach, chlorophyll and carotenoid content was higher in the 30 min
immersion treatment (Table 3).
The total amount of fructose was significantly higher in plants grown
under the optimal immersion time, plum included, but not in apple.
However, variations occurred in the fraction of free fructose depending on
the genotype and the treatment. Cherry and peach plants grown in stationary
liquid conditions accumulated more free fructose than the control, plum
accumulated it to a lesser extent, while in apple the content was the same.
On the contrary, after the cultivation in TIS the bound fructose accumulated
as sucrose was increased compared to the control (Table 3).
4. Discussion
The multiplication rates of shoot cultures of the four species cultured in
TIS did not differ from those cultured on solid medium as controls. However
the plants cultured in TIS never showed hyperhydricity and apex necrosis.
On the contrary, stationary liquid condition induced a deterioration of the
plants, due to hyperhydricity and necrosis, and a critical decrease of the
multiplication rate in most cases. Hyperhydricity occurred in around 10% of
the controls, for all genotypes, but never in the TIS treatment. This claim is
supported by the reduced water content in temporarily immersed plants
versus the control. In contrast, the decreased water content observed in
stationary liquid medium was related to necrosis and plant death after 60
days. Only in plum water content reduction was absent and the plants
appeared more hyperhydric than necrotic. It is reported in the literature that
the positive effects of TIS are due to a better aeration and renewal of
chemical components at each immersion, otherwise limited in solid
condition by the agar matrix. In this way the risk of anoxia and